PDP-8.co.uk » restoration

H960 rebuild

Toby Russell — Thu, 16 Jul 2009 22:00:47 +0000

My PDP-8s have finally got a new home in the form of a very rusty H960 that I recovered in my recent haul. Before fitting my -8s into it I decided to strip and respray to bring it back to its former glory.

Here are the steps I went through to achieve this:

Thoroughly wire brushed all rusty areas to remove the scaly rust.
Further removed the rust using a flap disk mounted on a powerdrill.
Any remaining rust was neutralized with a rust inhibiter
All original labels were carefully masked
The rack was resprayed in 2 costs of grey primer followed by 4 coats of satin black paint.

I’m very pleased with the end results, huge improvement. Not perfect as the rust has left the metal work a little pock marked but still very acceptable.

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PDP-8/M Rebuild – part 4 – Reassembly and first power up

Toby Russell — Fri, 10 Apr 2009 14:31:25 +0000

Having reinstalled the power supply into the chassis, the console was put back into slot 1 and carefully reassembled.

The minimum board set was then installed consisting of:

Slot2: M8330 KK8-E timings
Slot3: M8300 KK8-E major registers
Slot4: M8310 KK8-E major register control
Slot 20: M8320 KK8-E bus loads

The machine was then powered on and LEDs on the console sprung into life. Some basic operation from the console was possible (I was able to set the PC) although bit 5 of the PC appears to be stuck off. I will have to investigate whether this is a fault on the console or not.

I also installed an 8KW core memory set and retested with this in place. With these boards in place, the PC was all bits high and could not be changed.

So still some way to go! The next step will be to establish if the KK8-E is fully working and track down the issue that is causing the bit 4 of the address bus to appear stuck low on the console.

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PDP-8/M Rebuild – part 2 – Chassis repaint

Toby Russell — Tue, 07 Apr 2009 16:53:27 +0000

The chassis had all internal components removed (after carefully photographing everything to aid in reassembly) before being sanded down. Any areas of rust were sanded back to bare metal.

Unfortunately I could not persuade the build label to come off of the chassis cleanly so this had to be sacraficed. Before I removed it I carefully took a scan of it by placing the chassis on a flat bed scanner. This will allow me to replace the label with a replica at the end of the rebuild.

The chassis was resprayed in 3 coats of grey primer and then 4 coats of matt black paint. I’m really happy with the results, although in some areas I should have spent longer sanding to get a really perfect finish.

[Show as slideshow]

PDP-8/M Rebuild – part 1 – Initial Inspection

Toby Russell — Tue, 31 Mar 2009 19:17:57 +0000

I’ve finally decided to bite the bullet and start the rebuilt of one of my OMNIBUS PDP-8s. I decided to start with the more challenging of the two using the theory that by tackling the worst I would be much better prepared for a simple rebuild of better condition machine.

An appraisel of the machine

Before commencing, I will carry out a thorough appraisel of the machine so we can get a measure of the job in hand:

Front View

The front panel is in reasonably good shape. The plexi is mostly unmarked and the surround isn’t too grimey or scuffed.

A few of the console switches have broken but most are repairable and I’ve been kindly given a few spares which will make up for the missing ones.

The Backplane

Inside, the box is mostly clean, a few rust blisters but nothing too worrying. The backplane looks in good shape.

The power supply has already been moved and I will detail this later in the post.

The build label

The build label reveals that the machine was once fitted with:

KK8E Processor
KL8E Serial Console
3 x MM8E core sets (giving 12KW of memory)

When the machine arrived it had no cards. I’ve since aquirred a KK8E, KL8E and RX8E. For memory I plan to use one of the MM8E sets from my other 8/M

Power Supply

The power supply arrived loose in the box. It isn’t too bad, although has received some somewhat rough patches during its life. One area of concern is the two missing power transistors at the front of the supply.

I plan to rebuild the machine in the following stages:

Power supply strip and rebuild
Clean and respray of chassis
Clean and repair of console
Reassembly of chassis/console/PSU and backplane
Commissioning of power supply
Installation and test of KK8E and MM8E
Installation of RX8E and connection to RX02 drive